Vegetation trimmer having a blowing function

Abstract

A vegetation trimmer (10) having a motor (20) with a motor output shaft (30), a cutting head (22) for cutting vegetation, and a gear mechanism (26, 34, 36, 38) for transmitting power from said motor output shaft (30) to the cutting head (22). The motor output shaft (30) has a gear mechanism with a pinion wheel and a fan (28) mounted thereon. The gear mechanism (26, 34, 36, 38) further comprises an internal gear wheel (26) engaging with the pinion wheel (34) and connected to the cutting head (22), whereby the cutting head (22) rotates in the same direction (B) as the fan does (D) during operation of the motor (20).

Description

FIELD OF THE INVENTION[0001]The present invention concerns a vegetation trimmer also having a blowing function. Vegetation trimmers are well known power tools comprising a cutting head suitable for use in cutting vegetation, such as grass. The cutting head typically comprises one or more rotating blades, in which case the trimmer is generally known as a brush cutter, or one or more rotating lines, in which case it is generally known as a string trimmer, or a combination of both one or more blades and cutting lines.[0002]Vegetation trimmers which also have a blowing function are known as well. In such a case, air is directed by a fan either to expel vegetation which has already been cut by the trimmer from around the cutting head or to collect the cut vegetation into a receptacle. An example of such a vegetation trimmer which has a combination of blades and cutting line and which also has a blowing function is described in U.S. Pat. Nos. 6,442,845 and 6,460,253 also in the name of th...

AI Technical Summary

Benefits of technology

[0008]Preferably, the fan is enclosed within a substantially equiangular spiral volute centred on the motor output shaft, wherein the volute has a first bearing for the pinion wheel centrally located on an end face of the volute and a second bearing for the internal gear wheel located on the same end face at an offset from the first bearing. A volute with the shape of an equiangular spiral is found to be the most efficient in capturing and directing air blown by the fan. If the end face of the volute is provided with bearings for the pinion wheel and the internal gear wheel in the manner described, the volute may then double-up in function, both as a volute and as a mounting plate for the gears. This minimizes the number of components of the vegetation trimmer, thereby reducing manufacturing costs.

[0009]In a preferred embodiment, the volute has an exit mouth connected to a duct having a substantially uniform cross-section mounted on a guard for the cutting head, and the duct has an air outlet located on a radial edge of the guard at a distance from a center of the guard which coincides with the swathe of a cutting element (such as a length of cutting line) mounted on the cutting head, when the cutting element is caused to rotate by operation of the motor. Guards are quite common components of vegetation trimmers, which are provided in order to protect users from the cutting elements when they are rotating, as well as from flying debris, to which momentum has been imparted by the cutting element. However, in such a case, air exiting the mouth of the volute will also be shielded from the cutting element by the guard, so it is necessary for the air from the volute to be redirected to a location on the guard where it will still be able to blow vegetation cut by the trimmer. A duct with a substantially uniform cross-section and mounted in the location as described above is found to be the most effective way of achieving this. By locating the air outlet of the duct at a similar distance from the centre of the guard as the swathe of the cutting element when it is rotating, air exiting the duct picks up vegetation which has been cut by the cutting element at its maximum tangential velocity, thereby blowing the vegetation furthest from the cutting head.

[0011]Since it would be extremely difficult to mold the duct and the guard as a single component, the duct must instead be mounted to the guard either during manufacture or during subsequent assembly by an end-user. However, this has the disadvantage that it creates a joint between the duct and the guard, through which air blown by the fan may escape by leakage, thereby reducing the amount of air exiting the air outlet of the duct and thus the overall efficiency of the air-blowing function of the trimmer. Accordingly, it is desirable that the duct should comprise a liner moulded as a single component which is able to direct the air from the volute to the air outlet of the duct without leakage, thereby maintaining the efficiency of the air-blowing function.

[0012]The efficiency of the air-blowing function may be maximized by locating the air outlet of the duct on the edge of the guard at a level which is parallel to a cutting element of the cutting head and with the air outlet oriented parallel to a radius of the cutting head, so that air exiting the duct blows tangentially to rotation of the cutting element during operation of the motor. In this way, vegetation cut by the cutting element, which is also ejected tangentially from the cutting head, is picked up by the tangential airflow in the most effective fashion and is blown away from the cutting head as desired.

[0013]Preferably, the exit mouth of the volute comprises a spout projecting from the end face of the volute in the direction of the cutting head. This has two advantages. Firstly, the presence of the spout makes it easier to engage the duct with the volute without leakage. Secondly, the fact that the spout projects from the end face of the volute in the direction of the cutting head also helps to bring the exit point of the air from the volute closer to the cutting head, allowing the duct to be made shallower and less sharply angled, which reduces losses in the efficiency of the airflow through the duct caused by friction.

Problems solved by technology

This creates the technical problem that any air blown by the fan would also move in an opposite direction to the cutting head, thus also tending to act in an opposite direction to momentum which has been imparted to vegetation cut by the cutting head and therefore failing to expel the cut vegetation away from the cutting head as desired.

As a result, until now, it has been impossible to provide a string trimmer having both a step-down gear mechanism for more effective cutting of vegetation on the one hand and a blowing function for expelling cut vegetation from around the cutting head on the other.

Vegetation trimmers with a step-down gear mechanism and a fan driven directly by a motor are of course already known, but in such cases, the fan is only used to provide cooling air to the motor (in which case the direction of the air blown by the fan is irrelevant to the cooling function), and not to provide a blowing function for expelling cut vegetation from around the cutting head of the trimmer as well.

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